The invention relates to a pilot switching valve apparatus for causing a valve spindle inserted in a valve chest having a plurality of ports, so as to be reciprocatively movable, to be displaced by feeding pilot pressures from pressure sources into the valve chest, respectively, to thereby effect switching of connection among the respective ports, and a method of switching a pilot switching valve.
With reference to a switching valve in which a valve spindle having a valve element provided around the periphery thereof is inserted in a valve chest inside a valve block so as to be reciprocatively movable, being repulsed in a return direction by an urging force of a return spring, and switching of connection among a plurality of ports communicating with the valve chest is effected by causing the valve spindle to undergo displacement against the urging force of the return spring, various types including one disclosed in Patent Document 1 are well known.
Among those types of switching valves, there is generally well known a switching valve in which, for effecting switching of connection among respective ports, a valve spindle is caused to undergo displacement against an urging force of a return spring by feeding a pilot pressure from positive pressure sources into a valve chest so as to act on the valve spindle. With such a pilot switching valve apparatus as above, however, if the pilot pressure is unintentionally fed into the valve chest by error due to malfunction of the positive pressure sources, and so forth, this will cause the switching valve as well to undergo malfunction, thereby executing switching of connection among the respective ports. Accordingly, in order to prevent such malfunction of the switching valve, there is the need for providing the switching valve apparatus with a particular safety circuit, in which case the configuration of the switching valve apparatus will become complex, posing a problem that a higher cost results.
[Patent Document 1]
Japanese Unexamined Patent Publication No. Sho 63 (1988)-106966